The present invention relates to a method for fabricating a semiconductor device that includes a fluorine-containing organic film having a low relative dielectric constant.
With recent remarkable progress in semiconductor process technology, finer semiconductor elements and metal interconnections with higher integration have been pursued. With this trend toward finer size and higher integration, signal delay at metal interconnections has come to greatly influence the operation speed of semiconductor integrated circuit in the above situation, desired is a technique of forming a fluorine-containing organic film (fluorocarbon film) that contains carbon atoms and fluorine atoms as main components and has a relative dielectric constant lower than that of an inorganic film such as a SiO2 film or a SiOF film.
A fluorine-containing organic film has a relative dielectric constant of about 2, which is lower than the relative dielectric constant of a SiOF film (about 3.5 to about 3.8). Accordingly, by depositing such a fluorine-containing organic film between metal interconnections or on the top surfaces of metal interconnections, signal delay at the metal interconnections can be reduced.
However, the fluorine-containing organic film deposited using a material gas containing fluorine described above is disadvantageously poor in denseness and thus insufficient in mechanical strength, heat resistance, chemical resistance, and the like.
In order to solve the above problem, Japanese Laid-Open Patent Publication No. 10-199976 proposes a method for densifying a fluorine-containing organic film to improve oxidation resistance and heat resistance in the following manner. A copolymer of a polytetrafluoroethylene resin or a cyclic fluorine resin and siloxane is dissolved in a fluorocarbon solvent. The resultant solution is applied to a substrate while rotating, to obtain a fluorine-containing organic film. The resultant fluorine-containing organic film is then subjected to annealing where the film is kept in an atmosphere of an inert gas such as nitrogen gas at a temperature of 400xc2x0 C. for 30 minutes.
The above conventional method has the following problems. After a fluorine-containing organic film is formed in a film formation apparatus such as a rotary application apparatus, the resultant substrate with the fluorine-containing organic film formed thereon must be transported from the film formation apparatus to an annealing apparatus for densifying the film by annealing. This complicates the process, and moreover arises the following problems. Particles may attach to the substrate during the transportation, resulting in lowering the yield. Also, the fluorine-containing organic film may absorb water in the atmosphere, and the absorbed water may react with free fluorine atoms in the film, forming hydrofluoric acid. The hydrofluoric acid may corrode metal interconnections.
In view of the above, the object of the present invention is allowing a fluorine-containing organic film to be densified without the necessity of transporting a substrate with the fluorine-containing organic film formed thereon from a film formation apparatus to another processing apparatus.
In order to attain the above object, the first method for fabricating a semiconductor device of the present invention includes the steps of: depositing a fluorine-containing organic film on a semiconductor substrate using a material gas containing fluorocarbon as a main component in a reactor chamber of a plasma processing apparatus; and densifying the fluorine-containing organic film by exposing the fluorine-containing organic film to plasma of a rare gas in the same reactor chamber.
According to the first method for fabricating a semiconductor device, the step of depositing a fluorine-containing organic film on a semiconductor substrate and the step of densifying the deposited fluorine-containing organic film are performed in the same reactor chamber. This eliminates the necessity of transporting the semiconductor substrate to an annealing apparatus for densifying. As a result, the number of process steps required is reduced. In addition, the possibility of attachment of particles during the transportation and thus reduction in yield is avoided.
In the first fabrication method, the step of depositing a fluorine-containing organic film preferably includes the step of depositing the fluorine-containing organic film while cooling the semiconductor substrate. This improves the deposition rate of the fluorine-containing organic film.
In the first fabrication method, the step of densifying the fluorine-containing organic film preferably includes the step of exposing the fluorine-containing organic film to the plasma of a rare gas in a state where the semiconductor substrate has moved toward a plasma generation region in the reactor chamber. This facilitates densifying of the fluorine-containing organic film.
The second method for fabricating a semiconductor device of the present invention includes the steps of: forming a mask pattern made of a resist film or an insulating film on a metal film deposited on a semiconductor substrate; dry-etching the metal film using the mask pattern to form a plurality of metal interconnections made of the metal film; depositing an interlayer insulating film made of a fluorine-containing organic film between the plurality of metal inter-connections and on top surfaces of the metal interconnections using a material gas containing fluorocarbon as a main component in a reactor chamber of a plasma processing apparatus; and densifying the fluorine-containing organic film by exposing the fluorine-containing organic film to plasma of a rare gas in the same reactor chamber.
According to the second method for fabricating a semi-conductor device, as in the first fabrication method, the necessity of transporting the semiconductor substrate to an annealing apparatus for densifying is eliminated. This reduces the number of process steps required. In addition, the problem of attachment of particles during the transportation and thus reduction in yield is avoided.
Moreover, according to the second fabrication method, since the necessity of transporting the semiconductor substrate to an annealing apparatus for densifying is eliminated, it is possible to avoid the problem that the fluorine-containing organic film may absorb water in the atmosphere and absorbed water may react with free fluorine atoms existing in the film, forming hydrofluoric acid. Thus, an occurrence of corrosion of metal interconnections with the hydrofluoric acid is prevented.
In the second fabrication method, the step of forming a mask pattern preferably includes the steps of: depositing the insulating film on the metal film; forming a resist pattern on the insulating film; and dry-etching the insulating film using the resist pattern to form the mask pattern, and the step of dry-etching the insulating film is performed in the same reactor chamber.
The step of dry-etching the insulating film is performed in the same reactor chamber as the step of depositing a fluorine-containing organic film and the step of densifying the fluorine-containing organic film. This further reduces the number of process steps and also the possibility of attachment of particles.
In the first or second fabrication method, the fluorocarbon is preferably. C5F8, C3F6, or C4F6.
All of C5F8 gas, C3F6 gas, and C4F6 gas have carbon-to-carbon double bonds. During film formation, carbon-to-carbon double bonds are dissociated, and resultant carbon atoms are bound with free fluorine atoms. This reduces the number of free fluorine atoms in the fluorine-containing organic film. The resultant deposited fluorine-containing organic film is denser than a fluorine-containing organic film deposited using any of other fluorocarbon gases. In addition, C5F8 gas, C3F6 gas, and C4F6 gas are short in atmospheric life and small in GWP100, and therefore do not easily cause global warming.
In the first or second fabrication method, the rare gas is preferably argon gas.
Argon gas is often added to a material gas for film formation since the deposition rate improves by adding argon gas to the material gas. Therefore, by using plasma of argon gas for densifying, the same rare gas can be used for both the film formation process and the densifying process. This makes easy to perform the film formation process and the densifying process in the same reactor chamber.